Lamp failure warning system for road vehicles

ABSTRACT

A lamp failure warning system for a road vehicle includes a pair of lamps the failure of which is to be monitored, and a switch for energising the lamps. Current sensing means is provided in series with the lamps for detecting failure of one lamp or the other, and when the switch is off current is passed through both lamps without illuminating them, and a warning is given if both lamps have failed.

United States Patent 1191 1111 3,753,224 Martin Au 14 1973 [54] LAMPFAILURE WARNING SYSTEM FOR 2,257,856 10/1941 Rady 340/251 X ROADVEHICLES 2,486,599 11/1949 Ho1lins..... 340/80 UX 2,764,752 9/1956Hollins 340/252 [7 Inventor: Rex Martin, Blackburn, g n 3,629,79912/1971 Birtwistle 340/52 R [73] Assignee: Joseph Lucas (Industries)Limited,

Birmingham, England Primary Examiner-John w. Caldwell 22 Filed: Apr. 211971 Assistant Examiner-Kenneth N. Leimer Anor Holman & Stem [211 App].No.: 135,889 my [30] Foreign Application Priority Data S RACT May 2,1970 Great Britain 21,208/70 A p failure warning System for a roadvehicle cludes a pair of lamps the failure of which is to be moni- [52]:LS. (i1 340/80, 340/7ii634O/12i; tored, and a switch for energising thelamps Current [51] Fm. C; 061 6 /67 sensing means is provided in serieswith the lamps for [58] Md 0 g 5 detecting failure of one lamp or theother, and when the switch is off current is passed through both lampswithout illuminating them, and a warning is given if [56] Reierenc bothlamps have failed.

UNITED STATES PATENTS 1,726,994 9/1929 Murray 340/251 X 3 Claims, 1Drawing Figure Patented Aug. 14, 1973 INVENOR" w:

This invention relates to lamp failure warning systems for roadvehicles.

A system according to the invention includes a pair of lamps the failureof which is to be monitored, a switch movable from a first position to asecond position to energise the lamps, current sensing means in serieswith the lamps for detecting failure of one lamp or the other andoperating a warning device, and means operable when said switch is inits first position for passing current through both lamps withoutilluminating them, and giving a warning if both lamps have failed.

Preferably, the warning is given by .energising the same warning lampthat is operated with the switch in its second position when one lampfails. In this case, diodes are provided for isolating the two testingcircuits from one another.

The accompanying drawing is a circuit diagram illustrating one exampleof the invention.

Referring to the drawing, a vehicle battery 11 has its negative terminalearthed, and its positive terminal connected through the vehicleignition switch 12 to the movable contact of a stop lamp switch 13 onthe vehicle. The stop lamp switch 13 when in what is normally its offposition, completes a circuit by way of a resistor 14 and a diode 15 toone side of a warning lamp 16, the other side of which is earthed. Whenthe switch 13 is moved to its on position, it connects the positivebattery terminal by way of the switch 12 to a point intermediate a pairof windingsv 17,18, the other ends of which are connected to earththrough the vehicle stop lamps 19,21 respectively. The junction of thewindings l7 and 18 is further connected to the junction of the resistor14 and diode 15 through a diode 20. The windings 17 and 18 control apair of contacts 22 which when closed complete a circuit from thejunction of the switches 12 and 13 through a resistor 23 and the lamp 16to earth. The contacts 22 are closed by magnetic unbalance between thewindings !7 and 18, but also by magnetic unbalance between a pair ofwindings 24 and 25, the junction of which is connected to the positivebattery terminal through a switch 26 controlling the side and tail lampsof the vehicle. The other end of the winding 24 is connected to earththrough the side and tail lamps 27, 28 on one side of the vehicle,whilst the other end of the winding 25 is connected to earth through theside and tail lamps 29,31 on theother side of the vehicle.

The warning lamp 16 is designed to operate at one half of the batteryvoltage, and the resistors 14 and 23 ensure that the correct voltage isapplied to the lamp 16. Assuming for the moment that the switch 26 isopened and the switch 12 is closed with the switch 13 in the positionshown, current flows through the resistor 14, and then through the diodeand the windings l7 and 18 to the lamps 19 and 21. Assuming both theselamps are operating satisfactorily, then current flowing through thediode 15 is insufficient to illuminate the lamp 16, or alternativelyilluminates the lamp 16 at very low intensity, depending on the wishesof the circuit designer. However, if both lamps 19 and 21 fail,

then no circuit is completed by way of the diode 20, and all the currentflowing through the resistor 14 flows through the diode 15 to energisethe lamp 16 which is illuminated to warn the driver that the lamps l9and 21 have both failed. If one only of the lamps 19 and 21 has failed,there will be an increased current flow through the lamp 16, but it willstill not be brightly.

When the switch 13 is moved to its closed position, no current flowsthrough the resistor 14, and the lamps 19 and 21 are energised by way ofthe windings l7 and 18 respectively. As long as both lamps 19 and 21 areoperating satisfactorily, the contacts 22 are open, but if one of thelamps 19,21 fails, then the resultant magnetic unbalance between thewindings l7 and 18 causes the contacts 22 to close, completing a circuitto the lamp 16 by way of the ignition switch 12.

When the switch 26 is closed, the lamps 27,28 and 29,31 are illuminatedby way of the windings 24 and 25 respectively. Failure of any one of thelamps 27,28,29,31 results in a magnetic unbalance between the windings24 and 25, again causing the contacts 22 to close to illuminate the lamp16. It will be appreciated that various degrees of illumination of thelamp 16 are obtained when various combinations of lamps fail, but themost important feature is that with the switch 13 in its normal positionas shown in the drawing, a warning is given if both lamps 19 and 21 havefailed.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

1. A lamp failure warning system for a road vehicle including a sourceof potential;

a first winding having first and second magnetically opposing coils, oneend of each coil being connected to a common point;

first and second lamps the failure of which is being monitored, saidlamps being connected to the respective other ends of the first andsecond coils;

a switch having first and second positions, said second positionconnecting the source of potential to the common point of the firstwinding to energize and light the first and second lamps;

switchingmeans responsive to magnetic unbalance between the first andsecond coils due to failure of one of the lamps;

a warning light connected through the switching means to the source ofpotential, said warning light being energized when the switching meansis activated due to said magnetic unbalance;

said switch in the first position connecting said illuminated verysource of potential through a resistance and a firstand a secondunidirectional means respectively to said common point and said warninglight; said warning light having a higher resistance than the first andsecond lamps whereby when the switch is in the first position currentpasses through the resistance and the first unidirectional means withoutilluminating the lamps, but if both lamps have failed, then currentpasses through the second unidirectional means to energize the warninglight. 2. The lamp' failure warning system of claim 1 wherein the firstand second unidirectional means are diodes.

3. The lamp failure warning system of claim 2 further including a secondwinding having third and fourth magnetically opposing coils, one end ofeach coil being connected to a common point;

a switch to apply potential to the common point of the second winding toenergize and light the pairs of lamps, and whereby failure of any of thelamps upsets the magnetic balance between the third and fourth coils toactivate the switching means and apply potential to the warning light.

1. A lamp failure warning system for a road vehicle including a sourceof potential; a first winding having first and second magneticallyopposing coils, one end of each coil being connected to a common point;first and second lamps the failure of which is being monitored, saidlamps being connected to the respective other ends of the first andsecond coils; a switch having first and second positions, said secondposition connecting the source of potential to the common point of thefirst winding to energize and light the first and second lamps;switching means responsive to magnetic unbalance between the first andsecond coils due to failure of one of the lamps; a warning lightconnected through the switching means to the source of potential, saidwarning light being energized when the switching means is activated dueto said magnetic unbalance; said switch in the first position connectingsaid source of potential through a resistance and a first and a secondunidirectional means respectively to said common point and said warninglight; said warning light having a higher resistance than the first andsecond lamps whereby when the switch is in the first position currentpasses through the resistance and the first unidirectional means withoutilluminating the lamps, but if both lamps have failed, then currentpasses through the second unidirectional means to energize the warninglight.
 2. The lamp failure warning system of claim 1 wherein the firstand second unidirectional means are diodes.
 3. The lamp failure warningsystem of claim 2 further including a second winding having third andfourth magnetically opposing coils, one end of each coil being connectedto a common point; a pair of lamps connected to the other end of thethird coil; another pair of lamps connected to the other end of thefourth coil; said switching means being responsive to magnetic unbalancebetween the third and fourth coils due to failure of any of the pairs oflamps; and a switch to apply potential to the common point of the secondwinding to energize and light the pairs of lamps, and whereby failure ofany of the lamps upsets the magnetic balance between the third andfourth coils to activate the switching means and apPly potential to thewarning light.